1. Field of the Invention
The present invention relates to a projection type display device, and particularly to a rear-projection type display device capable of correcting a distortion of an image projected to a screen.
2. Description of the Background Art
A projection type display device modulates a light outputted from a light source by means of a display device, forms an optical image corresponding to an image signal, and enlarges and projects the optical image to a screen by means of a projection lens, to thereby display a large-screen image. A rear-projection type display device is a projection type display device which projects an image from a rear side of a transmission type screen.
However, the projection type display device involves a problem that if a positional relationship between a screen and a projection device is misaligned, a projected image is distorted into a trapezoidal shape. Additionally, in the projection type display device, an optical component part such as a mirror is provided on an optical path extending from the projection device to the screen. Thus, the projection type display device also involves a problem that a distortion may occur in a display image due to optical characteristics of the optical component part. A projected image having the distortion caused by the optical characteristics of the optical component part has not only a trapezoidal shape but also a complicated shape in which a contour of the image is not a straight line.
To correct the distortion, it is necessary to accurately recognize a distortion amount. The distortion is measured in accordance with a distance of a position at which the projected image is displayed from a position in the screen at which the projected image should be displayed. For this purpose, there is a method of projecting to a screen an image including a detection point used for a correction and detecting a position of the detection point projected to the screen by using a detection device such as a camera. In order to increase an accuracy of the correction, it is necessary to display a plurality of detection points in each of an outer peripheral portion and an interior portion of the image.
If the distortion amount is recognized, then the distortion is corrected by deforming an image-to-be-displayed such that the image can be correctly displayed if a distortion is added thereto.
Although the projection type display device is shipped from a factory with a distortion correction having been performed, a distortion newly occurs in an image due to, for example, a change in the positional relationship between the screen and the projection device which is caused by vibrations during transportation to a place where the projection type display device is actually used. Accordingly, a projection type display device capable of correcting a distortion even in a place of use is required. There is a method of installing an optical sensor as a detection device for detecting an image distortion in a projection type display device, detecting an image distortion by using an output from the optical sensor obtained when an image for a correction is projected, and correcting a detected distortion (see Japanese Patent Application Laid-Open No. 2008-268579). However, this method requires installation of a plurality of optical sensors for the correction of the distortion, which makes a structure complicated.